The invention generally relates to electric machines (e.g., an induction motor), and more particularly to methods of and apparatus for controlling electric machines.
Many methods and apparatuses are used to control an induction motor. Exemplary methods and apparatuses include speed tap changing, triac controls, and fixed speed drive. In changing the speed taps, an effective reduction in voltage or flux is provided to cause the motor to run at a reduced speed by the nature of a slip. The slip is a measurement of how much the movement of the rotor follows the excitation field, and is defined as the difference between the frequency of the excitation energy and the speed of the motor. While these controls provide adequate speed control, they do so at the expense of efficiency as the motor runs at a higher slip which is proportional to rotor conduction loss.
Electric machines (e.g., induction motors) are often utilized in heating, ventilation, and air conditioning (HVAC) systems to drive blowers that move fluid (e.g., air) through the system. Electric machines are also used in other applications (e.g., to drive fluid pumps) that require adjustment of a control parameter of the electric machine (e.g., speed, torque, fluid flow, and the like) to meet the system requirements.